<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>集合实践</title>
</head>
<body>
  <script>
    let arr = [1,2,3,4,5,4,3,2,1]
    //1,数组去重
    // let result = [...new Set(arr)];
    // console.log(result);

    //2.交集
    let arr2 = [4,5,6,5,6];
    // let result = [...new Set(arr)].filter(item=>{
    //   let s2 = new Set(arr2); // 4 5 6
    //   if(s2.has(item)){
    //     return true;
    //   }else{
    //     return false;
    //   }
    // });

    //简化
    // let result = [...new Set(arr)].filter(item => new Set(arr2).has(item));

    // console.log(result);

    //3.并集
    // let union = [...new Set([...arr,...arr2])];
    // console.log(union);

    //4.差集
    let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)));
      console.log(diff);
  </script>
</body>
</html>